Electric power transmission system



pt. 10, 194 E. F. w. ALEXANDERSON 2,213,945

ELECTRIC PQWER TRANSMISSION SYSTEM Filed Oct. 19, 1937 7 Sheets-Sheet 1 m m w wn n a r mu eN M i IF i E U a 5 4 re w a 5 Ll S p 0, 1940- E. F. w. ALEXANDERSON 2,213,945

ELECTRIC POWER TRANSMISSION SYSTEM Filed Oct. 19, 193'! 7 Sheets-Sheet 2 Ernst FTW. Alexanderson, m J g; 3:; 5; Hi Attorfiey.

Sept. 10, 1940.

E. F. W. ALEXANDERSON ELECTRIC POWER TRANSMISSION SYSTEM Filed Oct. 19, 1937 F132. IZ.

Inven Ern st F. W.. Ale

by His tt 7 Sheets-Sheet 3 ow-Tweg.

l 10, 1940- s. F. w. ALEXANDERSON 2,213,945

amcmzc rowan mmsmzssxon SYSTEM Fxled Oct 19, 1937 7 Sheets-Sheet 4 Inventor: Ernst F W Alex nd rson,

b H is Attornegp 0, 1940. E. F. w. ALEXANDERSON 2,213,945

ELECTRIC POWER TRANSMISSION SYSTEM F1166. oct. 19, 1937 Sheets-Sheet 5 Al exanderso Invent or Ernst F. W 3

a7 His AttOFneg.

#4 y w MK Q Km KR Q k w llwwkillllw ww m Sept. 10, 1940- E. F. w. ALEXANDERSON 2,213,945

ELECTRIC POWER TRANSMISSIQN SYSTEM Filed Oct. 19, 1937 7 Sheets-Sheet 6 Inventbr: Ernst FW. Alexander'son, y K d/M76.

His At torney.

Patented Sept. 10, 1940 ELECTRIC POWER TRAN SIVHSSION SYSTEM Ernst F. W. Alexanderson, Schenectady, N. Y., assignor to-General Electric Company, a corporation of New York Application camber 19, 1937, Serial No. 169,843

48 Claims.

My invention relates to electric power systems and more particularly to electric power transmission systems of the alternating current asynchronous ty-pe.

With the ever increasing demand for the transmission of electrical power over greater distances and with the coincident requirement for the transmission of larger blocks of power over existing alternating current transmission systems, it has become evident that there is a decided need for improved electric powergeneration and transmission systems of the type which are not inherently limited by the characteristics of synchronous-to-synchronous transmission. As is well known, in alternating current transmission systems of the synchronous type, the steady state power limit, as Well as the transient power limit, are dependent upon the angular displacement between the sending-end voltages and the receiving-end voltages of the systems.

In view of the recent importance attributed to a more comprehensive water power development in this country, it has become evident that it is highly desirable to employ asynchronous alternating current transmission systems in order to meet these requirements without sacrificing the desired flexibility of operation and the continuity of service required in large power developments.

As a further consideration, it is important that advantages of the induction generator.

For example, an induction generator with a low resistance squirrel cage winding, while not a synchronous machine, has transient synchronizing characteristics similar in many respects to those of a true synchronous machine due to the flux trapped in the squirrel cage winding. Therefore, the prior art typeof induction generator alone is not readily adaptable to asynchronous operation because of its pseudo-synchronous characteristics.

transient Furthermore, the prior art in provide a new and improved electric valve freduction generators must be associated with synchronous condensers or capacitors to furnish the magnetizing current, and the resultant or overall transient characteristics of such an assembly are so similar to the corresponding characteristics of a synchronous generator that the benefits derived were not great. Since the advent of electric valve converting means and by virtue of the inherent flexibility of control incident thereto, the induction generator controlled and regulated in accordance with my invention may be operated to utilize completely the advantages of asynchronous power generation and transmission.

It is an object of my invention to provide a new. and improved electric power transmission system.

It is another object of my invention to provide a new and improved electric power transmission system of the asynchronous type.

It is a further object of my invention to provide a new method for operating alternating current transmission systems of the asynchronous type.

It is a still further object of my invention to provide a new and improved control system for 5 dynamo-electric machines of the induction type.

It is a still further object of my invention to provide a new and improved electric valve control system for induction generators.

It is a still further object of my invention to provide a new and improved control system for alternating current asynchronous power transmission systems.

It is a still further object of my invention to quency changing system.

In accordance with an illustrated embodiment of my invention, I provide a new and improved electric power transmission system of the asynchronous type in which an induction generator supplies electrical energy to a synchronous system through suitable transmission apparatus, and

in which the induction generator is controlled by an electric valve means connected in the rotor circuit thereof. The electric valve means controls the voltage and the power output of the induction generator. The induction generator may be operated above or below synchronism, and the electric valve means connected in the rotor circuit may be controlled to supply exciting current to the induction generator, thereby dispensing with the need for auxiliary apparatus such as capacitors or associated synchronous apparatus for supplying exciting current to the generator. The electric Valve means connected age which is employed to control the voltage andthe power generated by the induction generator.

In accordance with another feature of my invention, I provide an alternating current transmission system of the asynchronous type which may be employed to interconnect several syn-'- chronous systems. According to one arrangement, synchronous alternating current systems may be interconnected by means of a coupled synchronous motor and an asynchronous induction generator. On the other hand, the asyn chronous interconnecting link may comprise a synchronous generator and an asynchronous induction motor.

In another embodiment of my invention, I provide a control system including electric valve means for an induction generator in which the electric valve means controls the in-phase.com' ponent of current in the rotor winding and also establishes therein the exciting current for. the induction, generator. The control system, by controlling the in-phase component of current in the rotor winding, efiects control of the power output of the induction generator, thereby providing a highly satisfactory arrangement for con trolling the induction generator under variable load conditions. I

According to another feature of my invention, I provide an electric valve control system for controlling an operating condition or an electrical condition of a dynamo-electric machine of the induction type having stator windings and, rotor windings. The electric valve means may be connected to the alternating current circuit to which the stator winding is connected or it may be connected to a separate alternating current circuit. The electric valve means are provided with control members which control the conductivities thereof, and excitation circuits energize the control members to control the power interchange between the rotor winding and the alternating current circuit, and hence control an operating condition of the induction machine. As an additional feature, the periodic control voltages which are impressed on the control members are controlled in accordance with the voltage of one of the electric circuits and are shifted in phase in accordance with an electrical condition of the other of the electric circuits. For example, the periodic or alternating voltages impressed on the control members are shifted in phase'in accordance with the current of the rotor winding circuit. Suitable phase shifting arrangements are also provided to adjust the phase relation of the voltages impressed on the control members, thereby providing a highly desirable system for controlling the power factor at which power is interchanged between the rotor winding circuit and the alternating current circuits. When the dynamo-electric machine is operating as an induction generator above synchronous speed, the electric valve means may be controlled to supply excitation current to the induction generator thereby dispensing with the need for auxiliary. apparatus for supplying exciting current.

In accordance with a still further embodiment of my invention, I provide an electric valve system for operating a dynamo-electric machine of the inductiontype within a range of speeds extending from sub-synchronous operation tosoversynchronous operation. The system includes an alternating current pilot. generator which may be direct connected to the rotor of the induction machine for generating an alternating voltage the frequency of which varies in accordance with the speed of the machine. Excitation circuits for the electric valve means supply periodic alternating current voltages for rendering the electric valves conductive in a predetermined order and include means for producingan alternating vol-.- tage which varies in accordance with the voltage of an associated alternating current circuit, and means for combining the voltage of the pilot generator thereby to produce a voltage of beat frequency which, controls the electric valve means conjoint-1y in accordance with the electrical conditions of the alternating current circuit and the rotor winding of the induction machine. The voltage of beat frequency is modulated in accordance with the voltage of the rotor winding and hence controls the conductivity of the electric valve means to transmit power to or receive power from the rotor winding. The alternating current transferred is of substantially sinusoidal wave form.

In accordance with still further embodiments of my invention, I provide new and improved control or excitation circuits for electric valve means employed in frequency changing systems such as those described above in connection with the transfer of electric power between an alternatiIlg current circuit and the rotorwindingof a dynamo-electric machine of the induction type.

For a better understanding of my invention, reference may be had to the following description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims. Fig. 1 of the accompanying drawings diagrammatically illustrates an embodiment of my invention as applied to an asynchronous electric power generating and transmission system. Fig. 2 diagrammatically illustrates an embodiment of my invention as applied to an asynchronous electric power generating and transmission system and shows the excitation circuits for electric valve means included in the system, and Figs. 3 and 4 represent certain operating characteristics thereof. Fig. 5 diagrammatically illustrates another embodiment ofmy invention as applied to an asynchronous electric power transmission system including a dynamoelectric machine of the induction type and associated electric valve means in which the machine is operable as a motor or as a generator within a range of speeds extending from sub-synchronous to over-synchronous operation. Figs. 6-10 represent certain operating characteristics of the embodiment of my invention shown in Fig. 5. Figs. 11a and 11b illustrate a still further embodiment of my invention as applied to an asynchronous electric power transmission system in-:

tric power generating and transmission system including an induction generator for generating and transmitting electric power asynchronously. An induction generator I, including stator or primary windings 2 and rotor or secondary Windings 3, is employed to generate electric power asynchronously relative to an associated alternatirig current circuit d-whic\h may be connected to the induction generator I through a transmission line 5 and suitable transformers 6 and I. The terms primary and secondary for designating windings 2 and 3, respectively, are employed in accordance with the well known nomenclature established by the induction motor and induction generator arts. This nonmenclature has been adopted in order to facilitate the identification of the windings of an induction machine. Synchronous apparatus, such as a motor or generator 8 having stator windings 9 and a field circuit winding I0, may be connected to the alternating current circuit 4. Rotor winding 3 of induction generator] may be driven by any suitable prime mover, such as a steam turbine or waterwheel turbine II. The induction generator I, the prime mover II and the transformer 6 maybe located at the receiving end of the transmission system, and the transmission line 5 may be an electrically long line, that is, a transmission line of a quarter wave length or more in length.

In order to control the voltage and the power' generated by the induction generator I and to supply excitation current to the induction gen.- erator, I employ a mutator, such as the electric valve apparatus I2 including electric valves I3--3Il. The electric valves I3--30 are preferably of the type employing an ionizable medium such as a gas or a vapor and each includes an anode 3|, a cathode 32 and a control member 33. While-I have chosen to represent the electric valves I33IJ as being of the type having a single anode and a single cathode enclosed within a receptacle, it is to be understood that I may employ a plurality of rectifying or inve.ting devices each having a plurality of anodes and a single cathode. The control members 33 of the electric valves I3-30 may be energized by any of the excitation systems described hereinafter in connection with Figs. 2, 3, etc. It will be understood that electric valves l32l are oppositely disposed relative to electric valves 2230 and that thesegroups of electric valves are interconnected through suitable inductive reactances 34, 35 and 36. The electric valve apparatus including electric valves I3--30 is connected between the rotor winding 3 of induction generator I and an alternating current circuit 31 which may be a variable voltage circuit to control the power transmitted to or received from the rotor windings 3 of induction generator I, and hence to control the power produced by generator I.

As an arrangement for controlling'the voltage and the power supplied by generator I in accordance with an electrical condition of generator I or in accordance with an electrical condition, such as the power-of alternating current circuit 38 which is connected to the stator winding 2 of generator I, I employ a control circuit 39 which may be of any conventional type. The control circuit 39 may include a circuit 46 for producing an electrical quantity such as a voltage which varies in accordance with the power of circuit 38 or in accordance with the power generated by induction machine I, and may include asuitable arrangement such as an auxiliary alternating current machine M for varying the voltage of circuit 31. The auxiliary alternating currentmachine 4i may be directly connected to the rotating member of the induction generator I and may be arranged to operate as a variable voltage generator when the induction generator i is operating below synchronous speed, and may be arranged to operate as a variable voltage motor when the induction generator I is operating above 1932, on an application of M. S. Mead, Jr., and

which is assigned to the assignee of the present application. The circuit 40 includes a pair of electric valves 46 and 41, preferably of the high vacuum type-each having a pair of control members 48 and 49 which control the conductivities of these electric valves conjointly in accordance with the voltage and the current of circuit 38 to produce a voltage across resistances 50 and 5| which varies in accordance with the power of circuit 38. Resistances '50 and 5I may be provided .with adjustable contacts 52 for controlling the magnitude of the voltage produced by circuit 46. A transformer 53 impresses on control members 49 of electric valves 46 and 41 a voltage Which varies in accordance with the voltage of circuit 38, and a transformer 54 is employed to impress on control members 48 of electric valves 46 and 41 an alternating voltage which varies in accordance with the current of circuit 38. A voltage divider 55 maybe connected across the terminals of -the transformer 53 to control the magnitude of the voltages impressed on control members 49 and a transformer 56 may be interposed between current transformer 54 and control members 48 to obtain the desired voltage transformation. A suitable impedance element, such as a resistance 51, may be connected across the output terminals of transformer 54 to limit the voltage thereof. A suitable source of unidirectional voltage, such as a battery, 58, may be connected between the common juncture of resistances 5B and 5| and cathodes of electric valves 46 and 41, and a suitable negative unidirectional biasing potential may be supplied by a battery 59.

While I have illustrated my invention as comprising a circuit for providingan electrical quantity which varies in accordance with the power of one phase of the circuit 38 or in accordance with the power of one phase of the induction generator I, it is to be understood that I may employ a circuit in which an electrical quantity proportional to the three phase power is utilized to control the induction generator I. As an agency for controlling the voltage of circuit 31 and hence as an agency for controlling the power produced by induction generator I in accordance with the power of circuit 38, I- employ a suitable controlling or regulating circuit 66 which controls the excitation of the field winding 43 of the alternating current machine 4|. The regulating system may comprise an exciter 6i having an armature 62 and a field winding 63,

a sub-exciter 64 having an armature 65 and a field winding 66, a field'regulating resistance 61 for the field 66 of the sub-exciter 64, and a suit- .able voltage controlling meanssuch as a regu- 4 to the output voltage of circuit 30, which voltage varies in accordance with the power of cir-., cuit '38. A switch 72. is connected between resistances D and 5! and coil H to permit the disconnection of the coil H from circuit ll). The

lower contact 69 of the regulator 68 is balanced by a weight 13 and the upper contact 69 is'biased downwardly by a suitable means, such as a spring 13" which may be connected to the supporting arm for the lower'contact 69.

While the control circuit 39 has been shown and described as comprising a particular type of circuit for providing an electrical quantity-which ,varies in accordance with the power of circuit 33 or in accordance with the power generated by induction machine I, it is to be understood that I may employ any suitable arrangement known in the art. Furthermore, it is to be understood that I may employ any other suitable arrangement for controlling the voltage of circuit 37, and hence the voltage of the generator l, in accordance with the power of circuit 38 or the power generated by induction genera ator i.

The general principles of operation of the embodiment of my invention diagrammatically shown in Fig. 1 will first be considered. Although the induction generator may be driven within a range of speeds extending from subsynchronous operation to over-synchronous operation and extending through synchronous operation, my invention will be described considering the induction generator operating at a speed above synchronism. Heretofore in the operation of induction generators, the slip frequency of the induction generator has been a relatively small percentage of the statorfrequency.- When an induction generator is operated under these conditions, although it generates power asynchronously, the induction generator possesses certain pseudo-synchronous transient operating conditions which limit. the benefits obtainable by the employment of the induction generator operating at greater slip frequencies. Where the induction generator has a relatively low resistance rotor winding, the field flux trapped in the rotor gives to the induction generator certain pseudo-synchronous transient characteristics which are not desirable. Therefore, 'I excite the induction generator l in a manner to obviate these difficulties and supply to the rotor winding 3 an alternating current of a frequency substantially greater than the natural oscillation frequency of the system including the receiving apparatus, the transmission line and the induction generator. I have found that in a 60 cycle alternating current system satisfactory operation is obtainable by producing in the rotor winding of the induction generator an alternating current of a frequency of approxicharacteristics.

Of course, the exciting current for the induction generator I may be supplied from synchronous apparatus or capacitors connected to the induction generator or connected to the transmission system. However, in accordancewith one embodiment of my invention, namely that shown-in Fig. 2 of the accompanying drawings and to be described hereinafter, the electric valve apparatus i33il may be employed .to supply excitation current to the induction machine R,

thereby reducing to a minimum, the amount of auxiliary exciting apparatus required or even in some instances dispensing altogether with such apparatus.

As will be explained hereinafter in connection with other embodiments of my invention, the electric valve apparatus including electric valves ,l3-3ll may be controlled to control the power produced by induction generator l and may be controlled to supply excitation current to the generator i. As explained hereinafter, this dual control may be effected by control of the periodic or alternating voltages impressed on control members 33 of electric valves |3-'30. However, in connection with the explanation of the embodiment of my invention shown in Fig. 1, I have chosen to describe the operation of the system shown therein when the power output of the induction generator I is controlled by controlling the magnitude of the alternating voltages impressed on electric valves l3-3ll. As will be understood, the electric valves iii-3B control the transfer of power between circuit 37 and rotor winding 3. When the induction generator l is operating above synchronism, the

electric valves 13-30 transfer power from the rotor windings 3 to the auxiliary machine ti through the alternating current circuit 3 1, the

electric valves operating as a rectifier relative tothe induction generator may be controlled by controlling the voltage of circuit 31. When the voltage of circuit 37 is reduced, the net or resultant impedance of the rotor winding circuit is decreased, permitting a greater current to fiow in the rotor windings 3 and causing the induction generator'l to generate a corresponding greater amount of power. On the other hand,

when the voltage of circuit 3'! is increased, the I resultant impedance of the rotor winding circuit is increased effecting thereby a decrease in the rotor winding current and efiecting a decrease in the power supplied by generator l.

Concerning in particular the operation of the control circuit 39, a detailed description of the operation of. the circuit 30 may be obtained by referring to the above mentioned Mead patent. Generally speaking, the voltage appearing between the adjustable contacts 52 of resistances 5D and 5! varies in accordance with the true power of circuit 38, or in accordance with the power of induction generator l. After initial adjustment, the voltage regulating or controlling circuit 66 will respond to regulate the voltage of the alternating current machine M in accordance with the power of circuit 38. The engaging contacts 69 serve to short circuit intermittently the resistance Ell which is connected in series relation with field winding 66 of subexciter '63, and thereby control the current supplied to field winding 63 of exciter 6! which in turn controls the excitation of field winding 43 of alternating current machine i I In this manner it will be understood that I provide a system which automatically controls tion generator in accordance with a predetermined controlling influence, Such as the power of the system, thereby affording a fiexible'and reliable arrangement for controlling an induc tion generator under variable load conditions so with the operation of the system when the induction generator I is driven above synchronous speed, it is to be understood that the system will operate satisfactorily when the induction generator is operating below synchronous speed. Whenthe induction generator is driven below synchronous speed, the alternating current machine 4I in conjunction with the electric valve apparatus I2 supplies power to the rotor windings 3 of induction generator I so that the induction generator I produces power. Under such conditions of operation, it is necessary that the rotating field produced by the rotor windings 3 revolve in a direction opposite to that produced by the stator windings 2. Since power is transmitted to the rotor windings 3 under this condition of operation, the auxiliary alternating current machine 4I operates as a generator driven by the turbine II. Where it is desired that the induction generator be susceptible of operating below and above synchronous speed, that is to permit the flow of power in both directions between rotor windirgs 3 and the auxiliary generator 4|, the

control members 33 of electric valves I330 may be energized by excitation systems of the type shown in Fig. 5.

In Fig. 2 of the accompanying drawings there is diagrammatically shown another embodiment of my invention for controlling a dynamo-electric machine of the induction type. The system shown in Fig. 2 may be employed for generating and transmitting electrical energy asynchronously. The prime mover, the electric valves, the induction generator, the transmission line and associated synchronous apparatus have been assigned reference numerals corresponding to like elements shown in Fig. 1. The rotor windings 3 of the induction generator I are energized from a suitable alternating current circuit I4 through the electric valve apparatus including electric valves I330 which corresponds to the electric valve apparatus I2 in Fig. 1. It is to be understood that the circuit I4 may be connected to the stator windings 2 where suitable apparatus such as capacitances and synchronous apparatus are available to supply exciting current to the induction generator.

In order to effect transfer of power from the rotor windings 3 to the alternating current circuit I4 conjointly in accordance with different electrical conditions, such as the voltages of the rotor windings 3 and circuit I4, I employ a plurality of excitation circuits I592 each of which includes a transformer 93, a suitable source of negative biasing potential such as a battery 94,

and a current limiting resistance 95 which is connected in series relation with the associated control member 33. To impress on control members 33 of electric valves I330 periodic voltages such as alternating voltages which vary in accordance with the voltage of circuit I4 and in accordance with an electrical condition such as the current or the voltage of rotor windings 3, I provide a control circuit 98 which comprises a plurality of phase shifting circuits 91, 98 and. 99. Each of the phase shifting circuits 9I99 may be of the impedance type and may include a transformer I00 having a primary winding IOI and a secondary winding I02 provided with an electrical intermediate connection I03, a resistance I04 and a variable inductance I05 provided with control windings I06 and I0I. The variable inductance I05 may be of the saturable type having a magnetic core member, if desired. Control windings I0'I may be energized from any suitable source of direct current, such as a battery I03, through a resistance I09, to establish in the variable inductance I05 a component of unidirectional flux. In order to control the phase of the alternating voltages impressed on excitation circuits I592 and hence to control the power factor of the current interchange between rotor windings 3 and circuit I4, control windings I06 of phase shifting circuits 97-99 are energized in accordance with an electrical condition of the rotor windings 3, such as the current of these windings. In the arrangement diagrammatically illustrated, control windings I06 are energized in accordance with the current of rotor windings 3 through current transformers I I0, thereby shifting the phase of the alternating voltages impressed on control members 33 during each cycle of the rotor winding voltage to control the power factor of the current flowing in the rotor windings 3. Transformers I00 of phase shifting circuits 9I-99 may be energized from the alternating current circuit I4 through any suitable phase shifting device such as the rotary phase shifter III. The-phase shifter III controls the effective or resultant impedance of the rotor winding circuit of the induction generator I and hence permits control of the power produced by the in duction generator.

The operation of the embodiment of my invention diagrammatically illustrated in Fig. 2 will be considered when the system is operating to transmit energy to the alternating current circuit 4 and when the induction generator I is driven above synchronous speed by theturbine II. Under this condition of operation, since the induction generator is driven above synchronous speed, power will flow from the rotor windings 3 to the alternating current circuit I4 through electric valves I330. The alternating voltages impressed on excitation circuits I592 will be controlled to effect this transfer of power conjointly in accordance with the voltage of the rotor windings 3 and the voltage of the circuit I4. Phase shifting circuits 9I99 of the control circuit 96 modulate the phase of the alternating voltages impressed on control members 33 to control the 'power factor at which power is transmitted to circuit I4 from rotor windings 3. The wave form of the current transferred is substantially sinusoidal. Let is be assumed that the induction generator I is driven at a speed so that the rotor winding frequency is approximately 10 per cent that of circuit I4. If the frequencyiof the alternating current .circuit 74 is substantially greater than that of the rotor windings 3, for example, if the frequency of the circuit I4 is 60 cycles and the frequency of the rotor winding current is 6 cycles, power may be transmitted from the rotor windings 3 to circuit 14 and the current may be commutated' an inverter relative to the voltage of circuit I8. Since control windings I6 of phase shifting circuits 9'i-99 are energized in accordance with the current of rotor windings 3, the phase of the alternating voltages impressed on excitation circuits 15-92 is controlled during each cycle of voltage of the rotor winding circuit, thereby controlling the conductivities of the electric valves I33B during each cycle. ofthe rotor winding voltage. By the proper adjustment of the rotary phase shifter III and by the proper valve system establishes an exciting current in the rotor windings 3 and thereby improves the power factor of the induction generator I. By the proper adjustment of the rotary phase III, the electric valve'apparatus may be con--' trolled to supply substantially all the exciting current required for the induction generator I and thereby dispense with the need for auxiliary apparatus such as synchronous machines and capacitances for supplying the necessary exciting current for the induction generator.

The operation of the embodiment of my invention shown in Fig. 2 may be better understood by referring to the operating characteristics shown in Figs. 3 and4. Considering Fig. 3 in particular, the curve A represents the output voltage of an electric valve for different phase displacements between the voltages impress-ed on the control members 33 and the voltages impressed on the anodes 3|. Since electric valves I3-30 are operated as inverters relative to the circuit, the phase of the alternating voltages impressed on excitation circuits Iii-92 through rotary phase shifter .I II is adjusted to lie with- C and D of Fig. 4 represent the three phase voltages of circuit 14 and curve E represents one phase of the alternating voltage of rotor windings 3 when the ratio between the frequency of circuit It and the frequency of rotor wind-- ings 3 is substantially 7:.1. The heavy curve F represents the opposing voltage in onephase offered by the electric valves I3-30 to the flow of rotor winding current. It is understood that voltage mitted to the circuit 14 by rotor windings 3 may be controlled and hence the power factor of the power interchange may also be controlled. For the conditions'of operation shown by the curves of Fig. 4, the' current transmitted to circuit 14 from rotor windings 3 will occur at substantiallyv unity power factor. If the phase shifting cir- 'cuits 91-99 are adjusted so that the phases of the alternating voltages impressed on centre; members 33 are advanced during the fore part each cycle of rotor winding voltage and retarded during the latter part, the opposing voltage ofiered by the electric valves .I3--30 will be decreased and increased during the respective portions of the wave, and hence the current in the rotor windings 3 willbe leading, in this poem. also permit control of shifter similar elements in Figs.

in the inverter range of operation. Curves B.

by controlling the wave shape of the opposing F the wave form of the current transphase shifter manner effecting an improvement in the power factor at which the induction generator I operates and also supplying excitation current to the induction generator I. It is to be understood thatthe amount of phase shift of the alternating voltages impressed on control members 33 during each cycle of voltage of the rotor -windings 3 may be controlled by the proper proportioning of the phase shifting circuits 9I-99.

Although the system diagrammatically shown in Fig. 2 has been explained for operation as an electric power generating andtransmitting system for operation of an induction generator above synchronous speed, it is to be understood that the system. will also operate as a motor controlling arrangement for an induction motor when in operation below synchronous speed. Under this condition of operation, the electric valves Iii-30 and the associated control equipv the power factor of the induction machine I.

In Fig. there is shown another embodiment of my invention for controlling a dynamo-electric machine of the induction type/to permit operation of the machine either as'an induction motor or as an induction generator above or below synchronous speed. The control system is shown as applied to anasynchronous electric power generator and transmission system. Elements of the arrangement of Fig. 5 have been assigned reference numerals corresponding to 1 and 2. Stator wind ings 2 of induction generator I are connected to an alternating current circuit. H2 and the rotating member of the induction generator I may be mechanically coupled to a synchronousdynamo-electric machine II3 having armature windings II and a field winding circuit II5 t'o..per-

mit asynchronous transfer of power between the alternating current circuit H2 and an alternating current circuit ,IIB. Depending upon direction of power transfer between circuits IIZ and H6, the dynamo-electric machine II3 may operate either as a synchronous motor or as a synchronous generator. Of-course, under corresponding'conditions the induction machine I will operate either as an induction generator or an induction motor. It is to be undertsoodthat circuit I4 may be connected to the alternating current circuit II2 if desired.

As an agency for controllingthe conductivi tiesof electric valves I3-30 in accordance with an electrical condition or operating condition of the induction machine I and in accordance with the voltage of alternating current circuit H2 or alternating current circuit IE, I provide a control or excitation system for energizing excitation circuits I5-92 to impress on control members 33 periodic or alternating voltages to render the electric valves conductive in a predetermined or-;

cordancewiththevoltage of circuit I I2, I provide a transformerII'I having primary windings I I8 and secondarywindings II9 which are provided with an electrical neutral connection 90.. A suitable phase shifting arrangement, such as a rotary I20, may be employed to control the phase of thiscomponent of .voltage impressed on the excitation circuits and hence control the energy component of current in rotor windings 3. In order to obtain an electrical quantity, such as an alternating voltage which varies in accordance with an operating condition such as the speed of the induction machine I, I provide an auxiliary or pilot alternating current generator I2I which may be mechanically connected to the rotating member of the induction machine I. The pilot generator I2I comprises armature windings I22 and a field winding circuit I23. Due to the fact that the pilot generator I2I is directly connected to the induction machine I, the frequency of the output voltage thereof will vary in accordance with the speed of the machine I and the voltage produced by the pilot generator I is introduced in the excitation circuits I5-92 through a transformer I24 and transformer Ill. The transformer I24 includes primary windings I25 and secondary windings I26 which are connected to provide a neutral connection I21. Neutral connection II9a of the transformer II! is connected to the neutral connection I21 of transformer I24 so that the voltage components provided by these transformers act in series relation and impress on excitation circuits -92, and hence impress on the associated control members 33, alternating voltages of beat frequency. Secondary windings H9 and I26 of transformers Ill and I24, respectively, are connected to excitation circuits 1592 in a manner to permit the transfer of power in either direction between rotor windings 3 and circuit I4 or II2. Of course, the frequency of the envelope of the beat voltage is at all times equal to the slip frequency of the induction machine I, or, in other words, equal to the frequency of the current in rotor windings 3. .A suitable phase shifting arrangement such as a rotary phase shifter I28 may be interposed between the pilot generator I2I and thetrans- I former I24 to control the phase displacement between the components of voltage provided by transformer Ill and transformer I24 and thereby control the power factor of the current in rotor windings 3.

The general principles of operation of the embodiment of my invention shown in Fig. 5 will be explained by considering the system thereof when power is being transmitted between alternating current circuits H2 and H6. If it be assumed that the power is transferred from circuit II2 to circuit H6, the machine I, of course, operates as an induction motor and the machine II3 operates as a synchronous generator. Due to the fact that the machine I is of the induction type, power may be transmitted asynchronously between circuits H2 and H6. The control system for the electric valves I3-30 controls the conductivities of these valves to effect energization of the rotor windings 3 irrespective of the angular position of these windings relative to the voltage of the alternating current circuit [I2 and hence removes the'inherent limitations of synchronous-to-synchronous transmission.

For example, if it is desired to transmit power asynchronously from circuit II2 to circuit IIB, the system may be arranged so that the induction "machine I operates as a motor and the machine II3 operates as a generator. that the circuit I I2 operates at 60 cycles and that thealternating current circuit IIB operates at 25 cycles, the synchronous machine Il3 may be designed to have six poles and arranged to operate at 500 R. P. M. Under these conditions, the induction machine I may be designed to have six- If it be asstnned teen poles and arranged to operate at 500R. P. M. The induction machine I, therefore, must be operated above synchronism and energy must be supplied to the rotor windings 3 from circuit H2 or circuit 14 through the electric valves I 3-30, and the electric valves in conjunction with the associated control circuit must establish alternating current in the rotor windings 3 at a frequency. of six cycles. In this manner power will be transmitted from circuit H2 to circuit I I6 asynchronously, thereby obviating the limitations of synchronous-to-synchronous transmission.

Considering in particular the operation of the arrangement of Fig. 5, the resultant control voltage impressed on excitation circuits 'I592 is of a beat frequency established by the difference of the alternating component produced by transformer Ill and the alternating component produced by the auxiliary or pilot generator I2I.

Referring to the operating characteristics shown in Fig. 6, for operation above synchronous speed of the circuit II2 curve G represents the output voltage of the pilot generator I2I; the curve H represents the component of voltage introduced in the excitation circuits by transformer II! and which is derived from circuit H2 or circuit I4; and curve J represents the difference voltage or the beat frequency voltage obtained by subtracting the voltages represented by curves G and H. Of course, the beat frequency voltage as represented by curve J is the resultant voltage impressed on excitation circuits 15-92. The envelopes K and L .of the beat frequency voltage J describe an alternating voltage of a frequency corresponding to the frequency of the voltage or current of rotor windings 3. The envelopes K and L of the beat frequency voltage J describe an alternating voltage of a frequency corresponding to the frequency of the voltage or current of rotor windings 3. The envelopes K and L are of the shape of intersecting sine waves and having rounded maxima and sharp minima, and the portions of the envelopes K and L lying between the vertical lines a and b represent one complete cycle of voltage of one phase of the rotor windings 3. Line M represents the negative biasing voltage which is impressed on control members 33 by batteries 94 and establishes the intervals during the cycles of voltage of circuits I4 or H2 at which the electric valves I3-3Il are rendered conductive. In other words, the beat frequency voltage, as represented by curve J, is required to exceed the biasing potential in order to render the electric valves conductive.

Vector ON of Fig. 7 represents one component of voltage introduced in the excitation circuits by transformer I I1 and vector NP represents another component of voltage introduced in the excitation circuits by the pilot generator I2I through transformer I24. The resultant voltage OP is impressed on the control members 33 through excitation circuits 15-92 and, of course, corresponds to the beat frequency voltage represented by curve J of Fig. 6. Curve Q represents the polar diagram of the average power or average conductivity of a valve of the vapor electric discharge type with respect to the phase displacement between the anode and control member voltages. When the induction machine I is offerating above synchronous speed, the voltage as represented by vector NP rotates in a counterclockwise direction, as indicated by the arrow, and when the induction machine I is operating below synchronous speed the vector NP rotates in the clockwise direction, as represented by the arrow in Fig. 8. t

For the conditions of operation shown by the curves of Fig. 6, the machine I is operating above synchronism at a speed relative to the synchronous speed as established by circuit I I2 in a ratio of' 60:55. Fig. 9 represents two cycles of voltage of the rotor windings 3 of machine I; thedistance between the vertical lines a and b representing one cycle and the distance between the vertical lines b and representing another cycle.

When the induction machine I is operating below the synchronous speed established by. circuit I I2, the curve G of Fig. 6 represents the voltageof circuit H2 and the component of voltage introduced in excitation circuits 'I592 by transformer II'IT Curve H of Fig. 6 under this condition of operation represents the component of voltage introduced in the excitation circuits by the pilot generator I2 I. For operation below synchr'onous speed either as a motor or a generator,

the control system in Fig. 5 effects an improvement in the power factor of the current trans-- mitted between rotor windings 3 and circuit It or circuit 2 and thereby improves the power factor at which the induction machine I operates. This effect will be apparent by consideration of the operating characteristics shown in Fig. 6, since-the resultant voltage impressed on the control members 33, as represented by curve J ,-renders the electric valves fully conductive during the fore part of the voltage'waves of the rotor windings 3 and decreases the'conductivities of these valves near the latter part-of the rotor winding voltage waves, thereby causing the effective'rotor current to lead the rotor winding voltages. The wave form of the rotor current is substantially sinusoidal.

The manner in which the power factor of the machine I is improved for operation below synchronous speed will be readily understood by consideration of the vectors shown in Fig. 10, where the .vector 0V1 represents the voltage of one phase of the stator windings 2 and the vector 0V2 represents the voltage of the corresponding rotor phase. Vector OR represents the lagging component of current present in the stator windings 2 and includes the magnetizing current. Vector OS represents the leading currentpres'ent in-the rotor windings 3 referred to the primary or stator windings 2. Since the currents as represented by the vectors OR and OS, both referred to the stator windings 2, are in opposition, it is to.be

understood that the resultant quadrature lagging current of the stator windings 2 will be reduced in magnitude and therefore effect an improvement inpower factor.

The energy component of current in "the rotor windings 3 may be rcontrolled by adjustment of the rotary phase shifter I 2!! which controls the phase of the control voltages impressed on con-,.

trol members 33 relative to the voltages of alter nating current circuits I l orv I I2. By 'virtue of this phase shifting arrangement, the energy transferred between circuits II2 and IIS may be controlled. Rotary phase shifter I23 may be adjuste to control the phase relation between the alternating current components produced by transformer Ill and pilot generator I 2].

I28, the power factor of the current ,in rotfor windings 3 may becontrolled, thereby providing an expedient arrangement forkcontrol ling the quadrature or reactive component of power transmitted between circuits H2 and H6? y suitable adjustment of the rotary phase shifter Another important feature of the embodiment of my invention shown in Fig. 5 is the feature of the control system which permits operation 'of the induction motor I through synchronous speed. Since the pilot generator IZI supplies voltage at synchronous speed and since the voltage introduced in the excitation circuitsby transformer I I1 is available at all times, the resultant voltage impressed on the excitation circuits is of suitable value to control the electric valves I 3-30 to supply unidirectional current to rotor windings 3 of induction machine I. The other words, at synchronous speed unidirectional current is transmitted to the rotor windings 3 from circuit It or circuit II2 so that the induction machine at synchronous speed operates essentially as a synchronous machine.

Although the operation of the embodiment of my invention shownin Fig. 5 has been explained by considering the system when energy orpower is being transmitted from circuit I I2 to circuit II3, it is to be understood that the arrangement thereof also is capable of transmitting power or there is represented another embodiment of my invention as applied to an electric valve translating apparatus for controlling a dynamo-electric machine of the induction type. The elements of-Fi'gs. 11a and 111) have been assigned reference numerals corresponding to similar elements in Figs. 1, 2 and 5.

I provide a plurality of excitation circuits I29 I46 associated with: electric valves I330, respectively. I have found that precise and reliable control of the electric valves I330 may be obtained by rectifying the beat frequency voltage derived from the pilot generator I 2I and the component of voltage derived from circuit II2 through transformer I5I. More particularly, I have found that since the envelope of the beat frequency voltage has rounded maxima and peaked minima, precise control may be effected by utilizing the rectified beat frequency voltage as a biasing voltage to maintain the electric valvesnon-conductive except at the times of occurrence of the peaked or sharp m'inima. Excitation circuits I29I36 are arranged to. utilize this principle. Each 6f the excitation circuits I29Il6 includes a transformer I4] which is energized from the alternating current circuit IIZ through conductors I48 and through a suitable phase shifting arrangement such as a rotary phase shifter I49.. The voltages impressed on control members 33 by means of transformers. I3! is, of course, of afr'e-x quency corresponding to that of circuit I I2; It

is to be understood that instead of energizing the transformers I41 from circuit I I2, the transformers may be energized from any other suitable source of alternating current of proper phase and frequency. Each of the excitation circuits I 29 I 46 also includes a transformer I50 which introduces in the excitation circuits an'alternating voltage which varies in accordance with the beat frequency voltage produced by the pilot gen-' erator I2I and a component of voltage derived from the alternating current circuit II2 through transformer I5I which is provided with a primary winding I52 and secondary windings I53 and I54 having a neutral connection I55. Primary wind-- ing I52 of transformer I 5I may be connected to the alternating current circuit II2 through conductors I56 and through a suitable phase shifting device such as a rotary phase shifter I51. The resultant voltages produced by the pilot generator I2I and the transformer I5I are impressed on transformers I50 in excitation circuits I29 I46 through conductors I58. It will be noted since the groups of electric valves, such as electric valves I3-I5, I6-I8, and I9--2I are controlled by transformers I24 and I5I so that each group acts as a three phase rectifier relative to the circuit II2 to supply current to rotor windings 3, and that the groups of electric valves 22-24, 25--21, and 28--30 serve to return the current to circuit I I2. The valves in each group are rendered conductive simultaneously relative to the voltages of circuit I I2" due to the single phase transformer I5I in the control system. Each of the excitation circuits I29I46 is also provided with a rectifier I59 which may be of the full wave type if desired, and Which rectifies the beat frequency voltage introduced in the excitation circuits by transformers I50. The output current of the rectifiers I59 is transmitted through-a suitable impedance element such as a resistance I60 and an inductance I6I to produce across the terminals of resistance I60 a unidirectional biasing voltage which varies in acc0rdance with the beat frequency voltage and hence in accordance with the voltage or current of the rotor windings 3 of induction machine I. Resistances I60 are connected in series relation with secondary windings I62 of transformers I41 and the resultant voltage is impressed on the control members 33 of electric valves I3--30.

The general principles of operation of the embodiment of my invention shown in Figs. 11a and 112) are essentially the same as those explained in connection with the embodimentof my invention shown in Fig. 5. The excitation circuits I29I 46 operate in a different manner than the excitationo circuits of Fig. 5 and the operation of the former circuits will be considered in detail. If it be assumed that the induction machineI is driven by the turbine II below the synchronous speed established by circuit H2, in order for the machine I to operate as a generator power must be transmitted to the rotor windings 3 through the electric valves I330. Furthermore, let it be assumed that suitable auxiliary apparatus, such as capacitances or synchronous apparatus, are connected to the circuit II2 to supply excitation current to machine I. Under this condition of operation when power is being transmitted to the rotor windings 3, the electric valves I330 operate as an inverter relative to the rotor windings 3 and the electric valves I33 0 are rendered conductive in a predetermined order by the excitation circuits I29-I46. Transformers I50 and the associated rectifiers I59 introduce in the excita tion circuits a variable negative unidirectional biasing potential which varies in accordance with the beat frequency voltage established by the pilot generator I2I and transformer I5I. By an inspection of curves K and L of Fig. 6, it is understood that the envelope of the beat frequency voltage J is of the type having rounded maxima and sharp minima. At the points of sharp minima the voltages appearing across the terminals of resistances I60 decreases rapidly and permits the voltages introduced in the excitation circuits by the associated transformers I41 to render the electric valves conductive. Transformers I41 in the excitation circuits introduce positive voltages of rotary phase shifters I28 and I51.

predetermined times establishd by the relative phase displacement of the voltagesimpressed on transformers I50 and transformers I41. The adjustment of these components of alternating voltage may be obtained by the. proper positioning Electric valves I3--30 are rendered conductive when the negative unidirectional biasing potentials pro duced by transformers I50 and rectifiers I59 decrease. to values sufficiently small to permit the voltage produced by transformers I41 to render the electric valves conductive. In this wayit is understood that power is transmitted from circuit II2 to rotor windings 3 conjointly in accordance with the voltage of circuit H2 and in accordance with the voltage and frequencyof the rotor phase windings 3.

While the operation of the embodiment of my invention shown in Figs. 11a and 111) has been explained when the machine I is operating as an induction generator below synchronism, it is to be understood that the arrangement of Figs. 11a. and 11b will also operate satisfactorily when the machine I is operated as a motor above synchrohave been assigned reference numerals corresponding to similar elements in Figs. 11a and 111). In order to establish a negative unidirectional biasing potential which varies in accordance with the envelope of the beat frequency voltage; as represented by curves K and L of Fig. 6, I provide a capacitance I63 which is connected in series relation with the output voltage of rectifier I59 and which is energized in accordance with the beat frequency voltage through transformer I50. A suitable impedance such as a resistance I64 may be connected across the capacitance I63 to discharge the capacitance at a predetermined rate dependent upon the constants of the circuit and the relative frequencies of the supply circuit and the rotor winding circuit. Rectifier I59 is connected to capacitance I63 to establish thereon a charge which varies in accordance with the envelope of the beat voltage, and the capacitance I63 is connected to the associated control member 33 to impress thereon a negative biasing voltage. A suitable source of positive voltage such as a battery I65 is connected in series relation with the capacitance I63 and secondary winding I62 of transformer I41 to render the associated electric valve conductive when the biasing voltage decreases to a predetermined value and when the voltage of transformer I41 dictates such action.

I have found that the sharp minima may be utilized to effect precise and reliable control of the associated electric valves and the excitation circuits of Fig. 12 utilize this principle. During the portion of the rounded maxima of curves K and L of Fig. 6 the capacitance I63 is charged so that the capacitance I63 impresses a negative potential on control member 33 of the associated electric valve, maintaining the electric valve nonconductive. In the region of the'sharp minima the negative voltage produced by capacitance I63 decreases sharply to a value sufficiently small to permit the positive voltage supplied by battery 865 to render the associated electric valve l3 conductive when the voltage of transformer Hi1 is of proper polarity. The value of resistance Hi l is chosen so that the negative potential follows the envelope of the beat frequency voltage very precisely. Of course, the phase relation of the unidirectional biasing voltage relative to the voltage of the alternating current circuit l 12 may be positioned by the adjustment of the rotary phase shifter M9 of Fig. 11?), and the phase position of the voltage introduced in the excitation circuit by transformer l il may be adjusted by means of the rotary phase shifter of Fig. llb.

While I have shown and described my invention as applied to a particular systemof connections and as embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the'true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination, an electric transmission line, synchronous apparatus connected to the receiving end of said transmission line, asynchronous apparatus connected to the transmitting end of said transmission line and including an induction generator having a primary winding and a secondary winding and an electric valve means connected in a circuit for said secondary winding to control the power generated by said induction generator, said electric valve means comprising at least one control member, and means for impressing on said control member a voltage which varies as a resultant of an electrical condition of said transmission line and as an electrical conditionof said secondary winding to transmit power asynchronously between said transmission line and said induction generator.

2. In combination, an electric transmission line, synchronous apparatus connected to the receiving end of said transmission line, asynchro.'

nous apparatus connected to the transmitting end of said transmission line and including aninduction generator having primary and secondary windings, an alternating current circuit and electric valve means connected in a circuit for said secondary winding to control the power produced by said generator and to supply excitation current to said generator, said electric valve means'comprising at least one control member, and means for impressing'on said control member a voltage which varies as a resultant of an: electrical condition of said alternating current circuit and an electrical condition of said secondary winding to 1' transmit power asynchronously between said transmission line and said induction generator.

3. In anasynchronous transmission system, the combination of an electric transmission line,

synchronous apparatus connected to the receiving end .of said transmission line, and asynchronous apparatus connected to the transmitting end of said line comprising an induction generator having stator and rotor windings, an alternating current circuit, and electric valve means con- 5 nected between said circuit and said rotor to control the ,power generated by said generator and to establish an excitattion 'current in said rotor winding of a frequency greater than the naturaloscillation frequencyof the system.

'4. Ina-i1 asynchronous electric power system, the combination of an induction generator having relatively movable primary and secondary-windings, an alternating current circuit connected to one of the windings, a source of alternating current, electric valve energy conversion means connected between said source and the other of the windings to energize said generator to efiect transfer of power to said circuit, said electric valve being provided with a controlmember, and

an excitation circuit connected to said control member comprising means for impressing thereon a voltage which varies as a resultant of an electrito said' quency of said system to transmit electric power to said line.

6. In an asynchronous electric power transmission system including a transmission line, a dynamo-electric machine having primary and secondary windings and an electric valve means connected in circuit with the secondary winding, the method of operation which comprises rotating said secondary winding at a speed above synchronism and controlling the conductivity of the electric valve means to establish alternating current in said secondary winding at a frequency greater 1 than the natural oscillation frequency of said system to transmit electric power to said line.'

7. In an asynchronous electric power system, the combination of an alternating current circuit, an induction generator having primary and secondary windings, the primary winding being connected to said circuit, means for supplying variable amounts of exciting current to said induction generator, means comprising an electric valve means connected in circuit with the secondary winding to control the power output'of said generator, said electric valve means comprising a i control member, and an excitation circuit for said control member comprising means for impressing thereon a voltagewhich varies as a resultant of .the voltage of said circuit and an' electrical condition of said secondary winding to efiect asynchronous. transmission of power between said alter- .nating current circuit and said induction gener ator. I 8. In combination, an induction generator having a stator winding and a rotor winding, electric valve means connected to said rotor winding for controlling the resuultant impedance thereof to control the power output of said generator, and

means for controlling the voltage of said induc-.

tion generator. 9. In combination, an alternating current circuit, an induction generator having a stator winding and a rotor winding, said stator winding being connected to said circuit, a second alternating current circuit, an electric valve means connected between said second circuit and said rotor wind ing for transferring power therebetween, and means for controlling the voltage of said second circuit to control the voltage of said generator and the power generated thereby.

10. In combination, an alternating current circuit, an induction generator. having a stator I winding and a rotor winding, said stator winding ing current circuit, an electric valve means connected between said second circuit and said rotor winding for transferring power therebetween, and means for controlling the voltage of said sc'cond circuit to control the amount of power interchanged between said second circuit and said rotor winding.

11. In combination, an alternating current circuit, a dynamo-electric machine of the induction type having a stator winding and a rotor winding, said stator winding being connected to said circuit, a second alternating current circuit, an electric valve means connected between said second circuit and said rotor winding for controlling the transfer of power therebetween, and means for controlling the voltage of said second circuit in accordance with the power of said first mentioned circuit to control said dynamo electric machine.

12. In combination, an alternating current circuit, an induction generator. having a stator winding and a rotor winding, said stator winding being connected to said circuit, a second alternating current circuit, an electric valve means connected between said rotor winding and said second circuit to transfer power therebetween, and means for controlling the voltage of said second circuit in accordance with the power of said first circuit to efiect control of the power produced by said generator.

13. In combination, an induction generator having a stator winding and a rotor winding, an alternating current circuit, an electric valve means connected between said rotor winding and said circuit to transmit power from said rotor winding to said circuit and for controlling the resultant impedance of the rotor winding circuit, and meansfor controlling the voltage of said alternating current circuit to' control the power produced by said generator.

14. In combination, an alternating current circuit, an induction generator having a stator winding connected to said circuit and having a rotor winding, an auxiliary alternating current ma-.

chine mechanically coupled to said rotor winding, and an electric valve means connected between said rotor winding and said auxiliary machine to control the power output of said induction generator.

15. In combination, an alternating current circuit, an induction generator having a stator winding connected to said circuit and having a rotor winding, an auxiliary alternating current machine mechanically coupled to said rotor winding, an electric valve means connected between said rotor winding and said auxiliary machine for transmitting power therebetween, and means for controlling the conductivity of said electric valve means to control the reactive component of current in said rotor winding.

16. In combination, an alternating current circuit, an induction generator having a stator winding connected to said circuit and having a rotor winding, an auxiliary alternating current machine mechanically coupled to said rotor Winding, an electric valve means connected between said rotor winding and said auxiliary machine for transmitting power therebetween, and means for controlling the voltage of said auxiliary machine to control the in-phase component of current in said rotor winding.

17. In combination, an alternating current circuit, a dynamo-electric machine of the induction type having a stator winding connected to said circuit and having a rotor winding, an auxiliary alternating current machine mechanically coupled to said rotor winding, and an electric valve means connected between said rotor winding and said auxiliary machine to control the power output of said dynamo-electric machine.

18. In combination, an alternating current circuit, an induction generator having a stator winding connected to said circuit and having a rotor winding, an auxiliary alternating current machine mechanically coupled to said rotor, and an electric valve means connected between said rotor winding and said machine for transmitting power therebetween, said auxiliary machine being arranged to operate as a motor for operation of said induction generator above synchronous speed and being arranged to operate as a generator for operation of said induction generator below synchronous speed to transmit power to said rotor winding.

19. In combination, an alternating current circuit, a dynamo-electric machine of the induction type having a stator winding connected to said circuit and having a rotor winding, an. auxiliary alternating current machine of the synchronous type mechanically coupled to said rotor winding, an electric valve means connected between said rotor winding and said auxiliary machine for transmitting power therebetween, and means for controlling the voltage of said auxiliary machine to control the power output of said dynamo-electric machine.

20. In combination, an alternating current circuit, an induction generator. having a stator winding connected to said circuit and having a rotor winding, an auxiliary alternating current machine of the synchronous type mechanically coupled to said rotor winding, said auxiliary machine being provided with a field winding for controlling the voltage thereof, an electric valve means connected between said rotor winding and said machine for transmitting power therebetween, and means for controlling the energization of said field winding in accordance with an elec-.

trical condition of said alternating current circuit 'to control the power output of said induction generator 21. In combination, an alternating current circuit, an induction generator having relatively movable windings, one of said windings being connected to said circuit, means for rotating another of said windings above synchronous speed, and an electric valve means connected to said last mentioned winding to supply excitation current to said generator.

22. In combination, an alternating current circuit, an induction generator having relatively movable windings, one of said windings being connected to said circuit, means for rotating another of said windings above synchronous speed, and an electric valve means connected to said last mentioned winding to control the power supplied by said generator and to supply excitation cur-,- rent to said generator.

23. In combination, an alternating current circuit, an induction generator having a stator winding connected to said circuit and having a rotor winding, means for rotating the latter winding above synchronous speed, a second alternating current circuit, and an electric valve means connected between said second circuit and said rotor winding for controlling the power factor at which power is transmitted from said rotor winding to said second circuit.

24. In combination, an alternating current circuit, an induction generator having stator-and rotor windings, an electric valve means connected between the rotor winding and said circuit to transmit power therebetween, and means responsive to the voltage of said circuit and an electrical condition of said rotor winding for controlling said electric valve means to control the power factor of .the current interchange between said rotor winding and said circuit.

25. In combination, an alternating current circuit, an induction generator having stator and rotor windings, an electric valve means connected between the rotor winding and said circuit to transmit power therebetween, said electric valve means having control members for controlling the conductivities thereof, and means responsive to the voltage of said circuit and an electrical condition of said rotor winding for impressing on said control members periodic voltages to control the power factor at which power is transmitted between said rotor Winding and said circuit.'

26. In combination, an alternating current circuit, a dynamo-electric'machine of the induction type having a stator winding and a rotor winding, an electric valve means connected between said rotor winding and said circuit to transmit power therebetween, said electric valve means having a control member for controllingthe conductivity thereof, and an excitation circuit for energizing said control member comprising means for impressing on said control vmember a periodic voltage having a frequency equal to that of said alternating current circuit and means for phase modulating said periodic voltage in accordance with an electrical condition of said rotor winding.

27, In combination, an alternating current cir- I cuit, a dynamo-electric machine of the induction type having a stator winding and a rotor winding, a plurality of electric valve means connected between said rotor winding andrsaid circuit to transmit power therebetween, said electric ,valve means having control members for-controlling the conductivities thereof, and an excitation circuit for energizing said control members coinprising means for impressing on said control membersperiodic voltages and meansvfor controlling the phase of said periodic voltages relative to the voltage of said alternating current circuit during cycles of voltage of said rotor winding.

28. In combination, an alternating current circuit; a dynamo-electric machine of the induction type having a stator windingand a rotor winding, an electric valve means connected between said rotor winding and said circuit to transmitv power therebetween, said electric valve means having a control member for controlling the conductivity thereof, means responsive to the Y voltage'of saidcircuit and to the current of said rotor. winding for impressing on said control member a periodic voltage to control the im-' pedance of the rotor windingcircuit, and means for shifting the phase of said periodic voltage in accordance with the rotor current to control the power factor at which power is transmitted'between said alternaitng current circuit and said rotor winding. Y r

29, In combination, a synchronous alternat- Sing current system, a second synchronous alter-- nating current system, and asynchronous apparatus for interconnecting said systems comprising acoupled synchronous motor and an induction-generator .having stator and 'rotor-' windings, said motor being connected'toone of said-systems and said stator winding of said generator being connected to said second system an electrical condition of said acrea e and an electric valve means connected to said said induction motor being connected to said.

second alternating current circuit and means comprising an'electric valve means connected between the'rotor winding of said motor and said second circuit to control the power generated by said synchronous generator to transmit power asynchronously between said alternating current circuits;

31. In combination,

\ an alternating current circuit, a dynamoelectric machine of the inductiontype having a stator winding and a rotor winding, an electric valve means connected be;

tween said rotonwinding and said circuit to transmit power therebetween, said electric valve means having a control member for controlling '.the conductivity thereof, and'an excitation circuit for energizing said control member comprising means for impressing on saidgcontrol member a periodic voltage having a component which varies in accordance with the voltage of said circuit and a component which varies in accordance with the voltage of said rotor winding;

32. In combination, an alternating current circuit, a dynamo-electric machine of the induction type having a stator winding and a rotor winding,'a plurality of electric. valve means connected between said rotor winding and saidcircuitto-transmit power therebetween, said electric valve-means each having an anode and a' control member for controlling the conductivity thereof, and an excitation circuit for'energizing' the control members toeifect transfer of power between said alternating current circuit and said rotor winding conjointly in accordance with the voltage of said alternating current circuit and the voltage of said rotor winding comprising means for impressing on the control members periodic voltages each having a component Which' varies as the voltage of said circuit and a component which varies as the voltage of said rotor winding for controlling the phase of saidperiodic voltages relative to the associated anode voltages during cycles of the rotor winding voltage to'control the power factor at which power is transmitted between said alternating current circuit and said rotor winding.

' 33. .In combination, an alternating current circuit, a dynamo-electric machine of the induction type having astator winding connected to said alternating current circuit and having a rotorwinding, electric translating apparatus connected between said circuit and said rotor winding for transmitting power therebetween and comprising a plurality of electric valve means each having an anode and a control mem ber for controlling the conductivity thereof, and

. an excitation system forenergizing the control members comprising means for impressing on the control members periodic voltages each having a component which varies in accordance with the voltage of said alternating current circuit and a; component which varies in accordance with rotor windings and means for controlling the phase of said first mentionedcomponent relative to the anode-voltages to control the real component of power transmitted between said alternating current circuit and said rotor winding.

34. In combination, an alternating current circuit, a dynamo-electric machine of the induction type having a stator winding connected to said alternating current circuit and having a rotor winding, electric translating apparatus connected between said circuit and said rotor winding for transmitting power therebetween and comprising 'a plurality of electric valve means each having an anode and a control member for controlling the conductivity thereof, and an excitation system for energizing the control members comprising means for impressing on the control members periodic voltages each having a component which varies in accordance with the voltage of said alternating current circuit and a component which varies in accordance with an electrical condition of said rotor winding and means for controlling the phase of said second mentioned component of voltage to control the reactive component of power transmitted between said alternating current circuit and said rotor winding.

35. In combination, an alternating current circuit, a dynamo-electric machine of the induction type having a stator winding connected to said alternating current circuit .and having a rotor winding, electric translating apparatus connected between said circuit and said rotor winding for transmitting power therebetween and comprising a plurality of electric valve means each having an anode and a control member for controlling the conductivity thereof, and an excitation system for energizing the control members comprising means for impressing on the control membersperiodic voltages each having a component which varies in accordance with the voltage of said alternating current circuit and a component which varies in-accordance with an electrical condition of said rotorwmding, means for controlling the phase of said first mentioned component relative to the anode voltages to control the real component of power transmitted between the alternating current circuit and the rotor winding and means for controlling the phase ofsaid second mentioned component of voltage to control the reactive component of power transmitted between said alternating current circuit and said rotor winding.

36. In combination, an alternating current circuit, a second circuit, electric translating apparatus for transmitting power between saidcircuits and comprising a plurality of electric valve means each having an anode and a control member for controlling the conductivity thereof, and an excitation circuit for energizing the control members comprising means for producing a periodic voltage'which varies in accordance with an electrlcal condition of one of said circuits; means for producing a second periodic voltage the frequency of which varies in accordance with a controlling influence derived from the other of said circuits and means responsive to a periodic voltage of beat frequency produced by said periodic voltages for impressing on the control members control voltages to render said electric valve meansconductive in a predetermined order to effect transfer of power between said first mentioned and said second circuits. I

37. In combination, an alternating current circuit, asecond alternating current circuit, electric translating apparatus for transmitting power between said circuits and comprising a plurality of electric'valve means each having an anode and a control member, and a plurality of excitation circuits each associated with a different electric valve means for energizing the control members comprising means for producing a periodic voltage which varies in accordance with an electrical condition of one of said circuits and means for producing a periodic voltage the frequency of which varies in accordance with a' controlling influence derived from the other of said circuits, means responsive to a periodic voltage of beat frequency produced by said periodic voltages for impressing controlvoltages on said control members to render said electric valve means conductive in a predetermined order and means for controlling the phase relation of said first mentioned periodic voltage and said second periodic voltage to control the phase of said periodic voltage of beat frequency.

38. In combination, an alternating current circuit, a second circuit, electric translating apparatus connected between said circuits for effecting the transfer of power therebetween and comprising a plurality of electric valve means each having an anode and a control member, and a plurality of excitation circuits each associated with a different electric valve means and including means for produc ng a periodic voltage which varies in accordance with the voltage of said first mentioned circuit,'means for producing periodic voltages the frequency of which varies in accordance with a controlling influence derived from said second circuit, means for impressing on the associated control members biasing potentials tending to maintain the associated electric valve means no nconductive and means responsive to said periodic voltages for producing resultant beat voltages modulated in acccdance with the voltage of said second circuit to control the moments during cyclesof associated anode voltages at which the electric valves are render conductive.

39. In combination, an alternating current circuit, a dynamo-electric machine of the induction type having a stator winding connected to said circuit and having a rotor winding, a plurality of electric valve means connected between said circuit and said rotor winding for transmitting power therebetween and each comprising an anode and a control member, aplurality of excitation circuits each associated with a different electric valve means and each comprising means for producing a periodic voltage which varies in accordance with the voltage of said alternating current ,circuit, and means for introducing into said excitation" circuits periodic voltages which vary in accordance with the speed of said dynamo-electric machine to produce in said excitation circuits resultant beat voltages, said beat volt ages having envelopes which vary in accordance with the voltage of said rotor winding to direct transfer of power between said alternating current circuit and said rotor winding through said electric valve means. 1

40. In combination, an alternating current ciricuit, a dynamo-electric machine of the induction type having a stator winding connected to said circuit and having a rotor Winding, a plurality of electric valve means connected between said circuitand said rotor winding for transmitting power therebetween and each comprising an anode and a control member, a plurality of excitation circuits-each associated with a different elec- 

